One aspect of the invention relates to a machine having a rotor mounted rotatably about an axis of rotation, a rotor outer casing fixed to axial rotor shaft parts and surrounds a winding support having a superconductive winding. The rotor also has a holding to support the winding within the rotor outer casing, comprising, on a torque-transmitting side, a first rigid connecting device between the winding support and the rotor outer casing, and on the opposite side, a second connecting device, compensating for changes caused by the axial expansion of the winding support. Also provided is a cooling and thermally insulating unit to cool and thermally insulate the superconductive winding. According another aspect of the invention, a method to cool and thermally insulate the superconductive winding is provided. A corresponding machine is disclosed in DE 23 26 016 B2.
Electrical machines, in particular generators or motors, generally have a rotating field winding and a fixed stator winding. By using cryogenic and, in particular, superconductive conductors it is possible in this case to increase the current density and thus the specific output of the machine, for example, the output per kilogram of the machine's weight, and also to increase the efficiency of the machine.
Cryogenic windings of electrical machines generally have to be thermally insulated from the surroundings and kept at the required low temperature by a coolant. Effective thermal insulation, in this case, can only be achieved if the cryogenic parts of the machine are separated from the hot exterior as much as possible by a high vacuum with a residual gas pressure of generally below 10−3 mbar and if the connecting parts transfer as little heat as possible between these cryogenic parts and the hot exterior.
Two variants are known, in particular, for vacuum insulation of rotors having cryogenic armature windings and hot stator windings: In a first embodiment, the rotor has a hot outer casing and a closed-off vacuum space which rotates with the rotor. The vacuum space is intended here to surround the cryogenic area on all sides (cf., for example, “Siemens Forsch. u. Entwickl.-Ber.” (Siemens Research and Development Report), Vol. 5, 1976, No. 1, pages 10 to 16). However, there is an undesirable heat transfer to the cryogenic parts via supports extending through the vacuum space. In a second embodiment, the essentially cold rotor rotates in a high vacuum. Here, the outer boundary of the high-vacuum space is determined by the internal hole in the stator. Such an arrangement does however require high-vacuum-tight shaft seals between the rotor and the stator (cf., for example, DE 27 53 461 A).
In the case of the machine as described in the DE-B2 specification cited at the beginning, the first-mentioned embodiment is implemented. According to the rotor of this machine, the superconductive winding is located in the interior of an armature cryostat which forms, with the flange shafts attached, an outer casing for the rotor. Due to the fact that known superconductor material is used for the conductors of the winding, helium cooling is provided at an operating temperature of around 4 K. In contrast, the outer contour of the rotor outer casing is approximately at room temperature and may even be above this temperature when operating. The useful torque of the machine is generated in the rotor winding. The rotor winding is arranged in a cold winding support which is suspended or held in the rotor outer casing, acting as the cryostat, such that it is for its part insulated. Here, this suspension or holding on the drive side of the rotor must be stable enough to transmit the torque from the cold winding support to a drive-side shaft part. A corresponding, rigid connecting device for transmitting the torque must therefore be designed to be comparatively sturdy and be connected in a force-fitting manner to the winding support and the drive-side shaft part. At the same time, this connecting device undertakes the drive-side centering of the cold winding support. Hardly any torque is transmitted on the opposite rotor side, which is also referred to as the non-drive or operating side, since connections which are important for the operation of the machine, such as, for example, a coolant supply line, are provided on this side. Therefore, essentially only the functions of centering and thermal insulation need to be fulfilled here. Since, however, in a transition from room temperature to the operating temperature the axial length of the winding support is reduced by at least one millimeter in relation to the corresponding expansion of the rotor outer casing, the operating-side suspension must also ensure that there is a corresponding linear compensation. In the case of the machine disclosed in the DE-B2 specification cited at the beginning, radially extending disk-shaped connecting elements which permit a corresponding bending in the axial direction to compensate for expansion are therefore provided between the rotor outer casing and the winding support.
Similarly, in the case of the rotor disclosed in DE 27 17 580 A, too, of an electrical machine having a superconductive excitation winding, a corresponding radially extending connecting element which permits axial deformation is provided between a rotor outer casing and a winding support.
In addition to the metallic superconductor materials which have long been known, such as, for example, NbTi or Nb3Sn, as are used in the abovementioned machines, metal-oxide superconductor materials having transition temperatures of over 77 K have also been known since 1987. Conductors containing such high-Tc superconductor materials, which are also referred to as HTS materials, are being used in attempts to create superconductive windings for machines. Machines having this type of conductor also require a corresponding compensation for expansion in the axial direction due to the differences in temperature between the operating temperature of the superconductor material and the external temperature of the hotter rotor outer casing.